A transmitter power amplifier that is mounted in a wireless communication device is often used concomitantly with a wave detector circuit that generates a direct-current voltage corresponding the strength of an output signal (high-frequency signals) of the transmitter power amplifier, with the intention to optimize transmission power (power consumption control or spurious control) by adjusting, in accordance with a detected output (a direct-current voltage generated in the wave detector circuit being hereinafter referred to as “detected output”), the level of a transmitter signal that is inputted to the transmitter power amplifier. In particular, power amplifier ICs having amplifier circuits and wave detector circuits integrated thereinto are often mounted in small-size wireless communication devices such as wireless LAN terminals or WiMAX terminals.
Examples of such a transmitter power amplifier can be found in Patent Literatures 1 and 2, which disclose power amplifiers each including: a power amplifier circuit including a power-amplifying transistor; and a wave detector circuit including a wave detector diode having its anode terminal connected to a collector terminal of the power-amplifying transistor via a capacitor.
The power amplifier of Patent Literature 1 is provided with a current-amplifying transistor for supplying a bias current to a base terminal of the power-amplifying transistor and to the anode terminal of the wave detector diode, whereby a reduction in the amount of power that is used in the wave detector circuit and a reduction in noise that is caused by a crosstalk signal coming from the wave detector circuit are achieved.
Further, the power amplifier (semiconductor integrated circuit) of Patent Literature 2 is provided with a biasing transistor (referred to also as “emitter-follower transistor”) connected to the anode terminal of the wave detector diode, whereby an expansion in detection amplitude is achieved.